1. Field of the Invention
This invention relates to a method of, and an apparatus for, supplying a lead alloy to a casting machine, particularly of the type which is used for manufacturing grids for lead batteries.
2. Description or the Prior Art
Grids for lead batteries are manufactured from a lead alloy, such as an alloy of lead and antimony or calcium. A casting machine of the type to which a lead alloy is fed by gravity is usually used for manufacturing those grids.
A number of systems for supplying the casting machine with a molten lead alloy at a constant rate are known. A first type of known supply system makes use of the head resulting from the difference in height between a melting furnace and a casting machine. The melting furnace is situated at a higher level than the molten alloy inlet of the casting machine. A feed pipe is connected between the bottom of the melting furnace and the inlet of the casting machine. The feed pipe is provided with a valve which is opened and closed to provide an appropriate supply of the molten alloy to the casting machine. The feed pipe is always filled with the molten alloy and no oxidation, therefore, occurs in the molten alloy in the feed pipe. As this system does not employ any rotary or overflow mechanism, it is possible to restrict the generation of an oxide slag in the melting furnace. This system is, however, likely to present a serious problem if the feed pipe or the valve fails or is broken during operation of the system. Any such failure is likely to result in all the molten alloy flowing out of the melting furnace. Moreover, the melting furnace needs to be situated at such a height that it is comparatively difficult to supply ingots of lead, etc., into the furnace and remove any oxide slag therefrom.
In a second known supply system, identified as an overflow system, the melting furnace need not be installed at a particularly high level, but a rotary pump is employed for supplying a molten lead alloy from the furnace to the casting machine so that it may enter the machine by overflowing its molten alloy inlet. This system does not have any of the drawbacks of the system which employs a head of the molten alloy. However, when the operation of the pump is discontinued, the resulting siphon effect causes all the molten alloy to flow back from the molten alloy inlet of the casting machine and the feed pipe to the melting furnace, which is located at a lower level. Air thus enters the feed pipe through the molten alloy inlet of the casting machine and oxidizes the lead alloy remaining on the inner surface of the feed pipe to form an oxide slag. An alloy of lead and calcium presents a particularly great problem. Moreover, the rotary motion of the pump and the overflow of the molten alloy promote the growth of the oxide slag.
A third supply system is known which employs a dispenser valve. While this system is an improvement over the overflow system, it has the disadvantage that it is necessary to seal the valve with an inert gas and remove an oxide slag from the valve frequently, as the slag adhering to the valve causes the molten alloy to leak out.
There are known a number of methods for heating the feed pipe. For example, gas is burned below the pipe, or the pipe is heated by an electric heating element which is wrapped around the pipe and which is surrounded by a heat insulating material. All of these methods are, however, inefficient.